1. Field of the Invention
This invention relates in general to an apparatus for extending the range of batteries used in electrically powered vehicles, and in particular to a battery warmer for extending the range of battery life in electric mowers.
2. Prior Art
Golf course greens maintenance equipment have traditionally utilized internal combustion engines. A number of mowers are known in the art. Some are discussed in U.S. Pat. Nos. 3,429,110 and 4,021,996. Mowers with multiple or gang cutting units are the subject of U.S. Pat. Nos. 3,511,033, 3,668,844, 4,866,917 and 5,042,236. All of the mowers discussed in these patents, however, rely on internal combustion engines for power. These internal combustion engines run the risk that fuel or hydraulic fluid will leak from the vehicle and damage the grass.
Furthermore, the use of internal combustion engines has resulted in the inconvenience and the hazard of obtaining and storing the necessary fuel, as well as the inconvenience of servicing the engine. Finally, internal combustion engines create both noise and air pollution.
Taking into consideration the risks and concerns associated with internal combustion engines, battery-powered mowers are a viable option to conventional internal combustion powered mowers. Electric mowers are quiet in operation, do not produce polluting emissions, and eliminate the possibility of spilling fuel or hydraulic fluid onto the greens.
The current electric mowers on the market, however, are at a distinct disadvantage relative to their internal combustion counterparts: the area the electrically powered mowers can mow without returning to be recharged is limited by the range of the battery set. An electric vehicle's range, i.e., the amount of available current from its batteries is affected by the temperature of the batteries. The cooler the batteries, the shorter the range associated with the batteries. Greens mowers usually are stored in areas that can cool to temperatures lower than is most effective for batteries. If the batteries in the electric mower are maintained at a temperature below about 70.degree.+/-5.degree. Fahrenheit, the battery range decreases.
The electric powered mowers currently in the marketplace utilize eight 6-volt lead-acid deep cycle batteries. Lead acid batteries accumulate the most charge, and therefore, can operate over the greatest range when they are charged in an ambient temperature between about 70.degree. and 85.degree. Fahrenheit. Once the battery set has discharged, if more mowing is required, the operator must either re-charge the battery set, which can take around eight to twelve hours, or replace the discharged battery set with a charged, alternate battery set. Generally, the batteries in the battery set are anchored to the mower frame and held in place with a metal hold-down bracket. To remove the batteries, the hold-down must be removed, and the wiring from each battery must be removed. This process is time consuming and not conducive to efficiently mowing an entire golf course.
Accordingly, a need in the art arises for electric mowers that have longer battery ranges, i.e., mowers that can mow more greens without having to return to be recharged.